President of Iran Hassan Rouhani had words of praise for Iranian General Qassem Soleimani early this morning, hours after the top military general was killed in an airstrike in Iraq ordered by President Trump, and he promised to “take revenge for this heinous crime.”

Rouhani also said Iran would “raise the flag” of Soleimani, the head of the Islamic Revolutionary Guard Corps’ elite Quds Force, “in defense of the country’s territorial integrity and the fight against terrorism and extremism in the region.”

The Pentagon confirmed last night Trump had ordered the attack that killed Soleimani and other military officials at Baghdad International Airport. Iran’s top “shadow commander” was responsible for the deaths of hundreds of American and coalition service members and the wounding of thousands more, the State Department said.

The U.S. State Department issued a security alert this morning urging all U.S. citizens to “depart Iraq immediately” due to heightened tensions in the region.

“Due to Iranian-backed militia attacks at the U.S. Embassy compound, all consular operations are suspended. U.S. citizens should not approach the Embassy,” the alert said. The agency also shared phone numbers people concerned about U.S. citizens and other loved ones in Iraq could call toll free for information.

The State Department said the airstrike “was aimed at deterring future Iranian attack plans.”

“General Soleimani was actively developing plans to attack American diplomats and service members in Iraq and throughout the region. The United States will continue to take all necessary action to protect our people and our interests wherever they are around the world.”

Brigadier General Esmail Ghaani, who served as Soleimani’s deputy commander since 1997, will now take over the helm as head of the Quds Force, Reuters reported, citing Iranian state media.

Officials in New York City and Los Angeles announced they’re taking precautionary measures in anticipation of a possible retaliatory attack. New York City Mayor Bill de Blasio said yesterday he’d spoken with top NYPD officials about immediate steps the department could take “to be vigilant against this threat for a long time to come.” LAPD said it was monitoring the situation in Iran but affirmed there has been no credible threat to the city.

Tens of thousands of people have taken to the streets of Tehran today to protest Soleimani’s killing, chanting “Death to America” and holding up posters bearing his image. Similar demonstrations were held in a number of other Iranian cities.

U.S. Secretary of State Mike Pompeo also tweeted a video that he claimed showed Iraqis taking to the streets to celebrate the death of Soleimani. It was not immediately clear where or when the footage in the tweet was recorded.

Many Democrats admitted that no Americans would mourn Soleimani’s death but also raised concern that the escalation will put the U.S. on a crash course for a new conflict in the Mideast. House Speaker Nancy Pelosi released a statement saying that Trump ordered the airstrike “without the consultation of Congress.”

“American leaders’ highest priority is to protect American lives and interests,” her statement said. “But we cannot put the lives of American service members, diplomats and others further at risk by engaging in provocative and disproportionate actions. Tonight’s airstrike risks provoking further dangerous escalation of violence.”

An adviser to Rouhani also quickly warned Trump of retaliation from Tehran.

“Trump through his gamble has dragged the U.S. into the most dangerous situation in the region,” Hessameddin Ashena wrote on the social media app Telegram. “Whoever put his foot beyond the red line should be ready to face its consequences.”